β-delayed neutron emission probability measurements at RIKEN RIBF

G. G. Kiss

RIKEN Nishina Center for Accelerator-Based Science

Radioactive Isotope Physics Laboratory

(in behalf of the BRIKEN collaboration)

r process nucleosynthesis

J. Covan, Nature 440 1151, S. Goriely, PRL 111 242502

Nuclear Physics input:

• Masses – r process path (R. Surman)

• Shell structure – peak location

• T1/2, fission parameters, Pn

values –abundance distribution

Produces ~50% of the stable isotopes heavier than Iron

Site unknown:

Core collapse Supernovae or

Neutron Star Merger? (G. Martínez Pinedo, T. Kajino, S. Goriely)

Location of the peaks Smoothing the

abundance distribution

Forming the

Rare Earth Peak

A. Arcones, PRC 83 045809, A. Farouqi, APJ 712 1359,

R Surman, JPS conf. Proc. 6 010010 M. Mumpower, PRC 85 045801

The role of β-delayed neutrons

β-delayed neutrons

• The neutron emission probability Pn measures the fraction of β-strength above the neutron separation energy Sn

• For n-rich nuclei very far from stability T1/2 and Pn will provide (the only) access to nuclear structure information

• The Pn value is the % that the β-decay is followed by at least one neutron emission.

• The P1n value is the % that the β-decay is followed by one neutron emission.

• Pn= P1n+P2n+P3n+…

• P0n=100%-Pn

𝑃𝑛 = 𝑆𝛽 𝐸𝑥 𝑓(𝑄𝛽−𝐸𝑥)

Γ𝑛

Γ𝑛 + Γ𝛾 𝑑𝐸𝑥𝑄𝛽𝑆𝑛

𝑆𝛽 𝐸𝑥 𝑓 𝑄𝛽 − 𝐸𝑥 𝑑𝐸𝑥𝑄𝛽0

Available information for r process simulations

Energetically

possible

Experimental

information

Fraction

measured

Mass region

β1n 606 ~ 241 37.5% 8He-150La & 213,214Tl

β2n 295 ~ 24 8.1% 11Li-52K & 98,100Rb

β3n 104 ~ 4 3.8% 11Li, 17,19B, 23N

β4n 60 1 1.7% 17B

Lack of available data: (Jeff 3.1 vs number of isotopes with Qβn >0

(using known masses from AME12)

Distribution of the data:

• ~ 40% in the

non-fission

region (A < 75)

• ~ 33% for

nuclear industry

(Br, Kr, Rb, I, Cs,

Xe)

• No data above 150La except 213,214Tl

36 38 40 42 44 46 480

20

40

60

80

100

Pn[

%]

QRPA-FRDM

KTUY-GT2

HFD-EDM

Pn[

%]

40 42 44 46 48 50 52 540

20

40

60

80

100

neutron number [N]

neutron number [N]

29Cu

QRPA-FRDM

KTUY-GT2

HFD-EDM

PRL102 142502

PRC 82 025806

Z.Phys 340 419

25Mn

36 38 40 42 44 46 480

20

40

60

80

100

Pn[

%]

QRPA-FRDM

KTUY-GT2

HFD-EDMP

n[%

]

40 42 44 46 48 50 52 540

20

40

60

80

100

neutron number [N]

neutron number [N]

29Cu

QRPA-FRDM

KTUY-GT2

HFD-EDM

PRL102 142502

PRC 82 025806

Z.Phys 340 419

25Mn

46 48 50 52 54 56 580

20

40

60

80

100

Pn

[%]

neutron number [N]

P1n - exp.

P2n - exp.

P1n - theo.

P2n - theo.

P3n - theo

31Ga

Large differences:

P. Möller et el., PRC 67 (2003) 055802 K. Miernik et al., PRC88 (2013) 041301

What is BRIKEN?

β-delayed neutron emission probability

measurements at RIKEN

BRIKEN aims for a large scale survey of β decay parameters: Most exotic nuclei → RNC SRC + BiGRIPS (largest acceptance) spectrometer Largest detection efficiency → (most) Advanced Implantation Detector Array AIDA

→ The largest β-delayed neutron detector

RI separation RI identification

238U primary beam

345 MeV / nucleon & ~50μA

Decay setup

• AIDA: most advanced implantation array

– Accept 1 kHz implantation rate

– Several (6-7) highly (128 x 128) segmented DSSD

detectors

• BRIKEN: highest efficiency counter setup ever built

(~68%-76%)!

– 3He filled proportional counters from embedded in

a ~ 1m3 polyethylene moderator

ORNL (84), UPC (42), RIKEN (26), GSI (10)

– Flat efficiency curve led to minimalized

systematical uncertainty

– Hybrid geometry (148 tubes + 2 clovers)

– Compact geometry (166 tubes)

More details:

A. Tolose talk (Tuesday 12:50 - 13:10)

C. Griffin et al., Pos (NIC XIII) 097 (2014)

A. Tarifeño-Saldivia et al., JINST 12 P04006 (2017)

Scientific cases

Half-lives and beta delayed neutron

emission probabilities relevant to

understand the formation of the rare

earth r process peak

Measurement of β-delayed neutron emission

probabilities relevant to the A = 130 r-process

abundance peak

Decay properties of r-process nuclei in deformed region

around A = 100 ~ 125

Measurements of new beta-delayed neutron

emission properties around doubly-magic 78Ni

Title Approved

Length

[days]

Aims Spokespersons

Measurements of new beta-delayed

neutron emission properties around

doubly-magic 78Ni

3.5 ~ 20 new P1n &

~ 14 new P2n

K.P. Rykaczewski,

J. L. Tain,

R. Grzywacz,

I. Dillmann

Decay properties of r-process nuclei in

deformed region around A = 100 ~ 125

6.5 ~ 60 new P1n &

~ 30 new P2n

S. Nishimura,

A. Algora

Measurement of β-delayed neutron

emission probabilities relevant to the A =

130 r-process abundance peak

6.5 ~33 new P1n &

~ 6 new P2n &

A. Estrade,

G. Lorusso,

F. Montes

Half-lives and beta delayed neutron

emission probabilities relevant to

understand the formation of the rare

earth r process peak

10 ~ 36 new P1n G. G. Kiss,

A. Morales,

A. Tarifeño-Saldivia,

A. Estrade

To be submitted newt PAC meeting (2017 December)

Study of the multiple delayed neutron

emission

? 15 new P1n &

21 new P2n &

21 new P3n

I. Dillmann

Measurement of β-delayed neutron emission probabilities relevant to the A = 130 r-process

abundance peak

Low entropy

hot wind

High entropy

hot wind

cold wind

Neutron star

merger

Different T, ρn shifts the A ~ 130 peak!

Roederer, APJ. Lett. 747 L8, Mumpower, Prog. Part. Nucl. Phys. 86 86

6.5 days beamtime,

settings were centered on 130Ag (~4.5 d) and 149Xe (~1.5 d).

More than 25 P1n were measured for the first time, data

analysis is in progress (127Pd,131Ag, 133Cd…).

Located far from closed shells, new production mechanism is

needed!

The Origin of the Rare Earth Peak

1. Slower neutron capture in the peak region?

2. „Kink” in the separation energies?

3. Prompt / β-delayed fission?

R. Surman, PRL 79 1809; PRC 64 035801

M. Mumpower, PRC 85 045801, PRC 86 035803;

S. Goriely, PRL 111 242502

A. Arcones, PRC 83 045809;

T. Scafer, PRC 94 055802

C. Freiburghaus, Astrophys. J. 417 381

and further references therein.

150La (Z=57)

No Pn data!

213,214Tl (Z=81)

2.5 days beamtime, setting was centered

on 167Sm.

Several new P1n values and T1/2 were

measured

Summary

• β-delayed neutron emission probabilities are important for r process nucleosynthesis calculations

• There is lack of experimental data

• The BRIKEN collaboration aims a large scale survey of β decay parameters for isotopes located far from the valley of stability

• Measurements and data analysis are in progress

Thank you for your attention!

ご清聴ありがとうございました (Go seichō arigatōgozaimashita)

Grazie per la vostra

attenzione!

Köszönöm a figyelmet!